With about 66 scholarship players, Penn State has to be exceptionally careful with the health of its squad this year. Head coach Bill O'Brien has said he plans to use more "thud" and fewer tackling drills during training camp, and starters likely will get more rest and breaks in-season.

Still, injuries will happen. Before camp started, defensive end Brad Bars ruptured an Achilles tendon, which will sideline him this season. Bars likely would not have started, but he would have been part of a line rotation and would have played special teams. His loss is significant.

With that in mind, here are five players Penn State simply can't afford to lose.

1. Adrian Amos

The safety is among the team's most versatile defensive players. A converted cornerback, he can play all four secondary positions (five, including the nickel), as well as some linebacker. He'll be integral to special teams as well. Amos might see more snaps than anyone on the team.

2. Deion Barnes

The defensive end made six sacks last season and is poised to double that total. Primarily a speed rusher, Barnes said he wanted to improve his power game and run defense before camp. With Bars out, the Lions are thin on experience at defensive end. And Barnes is one of the Big Ten's best.

3. Mike Hull

Middle linebacker Glenn Carson is a third-year starter, but Hull will be the playmaker of the group this fall. After Mike Mauti's injury against Indiana, Hull made 11 tackles and a sack. He led Penn State's defensive reserves in tackles (58), broke up four passes and blocked a punt. Though he'll be a first-year starter, Hull is the No. 2 veteran at linebacker. And that position, with only five scholarship players, can afford no injuries.

4. DaQuan Jones

Gil Brandt of NFL.com called Jones the nation's top senior defensive tackle, hinting at a huge potential payday next spring. Jones won't have Jordan Hill alongside him this fall, so the double-teams that followed Hill will switch to Jones. But at 6-3, 318, he's strong and quick enough to handle them. Outside of Jones, though, nobody has played much at defensive tackle.

5. Allen Robinson

Finally, an offensive player. Penn State has more depth on offense, particularly at receiver and tight end, but Robinson is the group's primary playmaker. He caught 77 passes for 1,013 yards last year, and his emergence helped quarterback Matt McGloin feel more comfortable in tight spots. The Lions have talent at the skill positions but none of Robinson's caliber.